The present invention relates to a deterioration detecting method and a remaining capacity detecting method for an electrochemical device.
Electrochemical devices, such as batteries, capacitors, and electrochromic devices, are widely used in electric appliances and electronic appliances. In particular, batteries have been attracting a rapidly increasing attention recently with the spread of portable appliances, such as notebook computers, portable telephones, and video cameras, the increase in energy demand, the problem in global environment, and the like.
As batteries which are typical electrochemical devices, various types of batteries are known and they fall into two major categories of non-rechargeable primary batteries and rechargeable secondary batteries.
As the primary batteries, there are exemplified alkaline batteries, manganese batteries, lithium batteries, air-zinc batteries and the like. On the other hand, as the secondary batteries, there are exemplified lithium ion secondary batteries which are in rapid spread recently, nickel-metal hydride storage batteries which are used as a large power supply for electric cars and the like, nickel-cadmium storage batteries, lead-acid storage batteries, and the like.
As the alternative batteries, there are exemplified physical batteries such as fuel cells for generating electricity with fuel, solar cells for generating electricity with the sunlight, and thermoelectric exchange cells for generating electricity with earth heat or the like.
Presently desired is enhancement in the capacity and the energy density of batteries. Further, regarding secondary batteries, desired is improvement in charge/discharge cycle characteristics. In order to meet these requirements, development has been intensively made for the materials and the like to be used for these batteries.
When batteries are stored in a deeply-charged state for a long time or undergo charge/discharge cycles under a high ambient temperature, certain secondary batteries deteriorates, and hence the capacity thereof decreases. Once the capacity of the batteries has decreased, the original battery capacity does not recover even after sufficient charging. The reason of this is thought to be attributed to decomposition of the ion conductor in the electrolyte, irreversible chemical reactions in the interface between the ion conductor and the electrode active material, irreversible phase transition reactions of the electrode active material and the like. Such deterioration of batteries substantially depends on ambient temperature, duration of storing, charge/discharge cycle condition, and therefore it has hitherto been difficult to accurately estimate the degree of deterioration unless the batteries are disassembled.
Because of the above-mentioned difficulty in accurately estimating the degree of deterioration, accuracy has been also poor in the detection of remaining capacity of deteriorated batteries. In particular, accuracy has been much poorer in the detection of remaining capacity of batteries having undergone high temperature storing or repeated charge/discharge cycles.
An object of the present invention is to resolve the above-mentioned problems and provide a deterioration detecting method for accurately detecting the degree of deterioration of an electrochemical device such as a secondary battery and a remaining capacity detecting method for accurately detecting the remaining capacity even for a deteriorated electrochemical device.
The present invention relates to a deterioration detecting method for an electrochemical device comprising electrodes and an ion conductor, wherein an electrochemical characteristic of the electrochemical device is detected, and an obtained detection value indicating the electrochemical characteristic is then compared with a reference value indicating a standard electrochemical characteristic of the electrochemical device to estimate the degree of deterioration of the electrochemical device.
In the above method, it is effective that a model which expresses an electrochemical characteristic by a parameter of the electrochemical characteristic of a component of the electrochemical device, that a value of the parameter indicating the electrochemical characteristic of the component is calculated from a detection value obtained by detecting the electrochemical characteristic of the electrochemical device, and that the value of the parameter is compared with a reference value indicating a standard electrochemical characteristic of the component to estimate the degree of deterioration of the electrochemical device.
In particular, it is effective that the parameter is the sum of the internal resistance of the electrode and the internal resistance of the ion conductor.
With regard to the model, it is effective to use at least one selected from the group consisting of a potential model of the electrode, an electron transport model of the electrode, an ion transport model of the electrode, an ion transport model of the ion conductor, and a model representing an electrochemical reaction occurring in the interface between the electrode and the ion conductor.
Further, the present invention also relates to a remaining capacity detecting method, wherein a capacity value of the electrochemical device is estimated based on the degree of deterioration obtained by the deterioration detecting method for an electrochemical device, and a remaining capacity of the electrochemical device is calculated using the obtained capacity value.
Furthermore, the present invention relates to a charger comprising: a means for detecting an electrochemical characteristic of a battery; a means for estimating the degree of deterioration of the battery by comparing an obtained electrochemical characteristic with a standard electrochemical characteristic of the battery; and a means for controlling the charge of the battery based on the obtained degree of deterioration; and a discharge controlling apparatus comprising: a means for detecting an electrochemical characteristic of a battery; a means for estimating the degree of deterioration of the battery by comparing an obtained electrochemical characteristic with a standard electrochemical characteristic of the battery; and a means for controlling the discharge of the battery based on the obtained degree of deterioration.